1. Field of the Invention
The present invention relates to avian leukosis virus (ALV) subgroup J strain Hc1 envelope (env) gene and gene products for use in diagnosis and vaccine development.
2. Description of Related Art
Avian leukosis virus (ALV) is the most common naturally occurring avian retrovirus associated with neoplastic diseases and other production problems in chickens [Crittenden, Avian Pathol., 10:101-112 (1981); Payne and Fadley, Diseases of Poultry, 10th Ed., 414-466, (1997)]. It comprises eight subgroups based on envelope properties. This group of viruses is capable of inducing a variety of neoplasms, but lymphoid leukosis is the most common naturally occurring B-cell lymphoma of chickens. A newly emerged subgroup J (ALV-J) was first isolated in England in 1989 and in the United States in 1994. Infections caused by this virus reached epidemic proportions in 1996. The total loss in commercial broiler breeders is currently estimated to be 1.5% per week in excess of normal mortality and represents a major economic loss for the poultry industry. In view of these astounding numbers collected over the past five years, the newly emerging ALV-J has been elevated to the top of the disease priority list for the poultry broiler breeder industry.
ALV-J was first reported in the United Kingdom in 1991 and was found to be associated with myeloid leukosis (ML) in meat-type chickens [Payne et al., J. Gen. Virol., 72:801-807 (1991); Payne et al., Vet. Record, 129:447-448 (1991), Payne et al., Leukemia, 6:1167-1176, (1992); Payne et al., Avian Dis., 37:438-450, (1993)]. ALV Strain HPRS-103, the prototype of ALV-J appears to be a recombinant between ALV and ancient endogenous avian retroviral envelope (E51) sequences [Bai et al., J. Gen. Virol., 76:181-187 (1995); Bai et al., J. Virol., 69:779-784 (1995)]. Because ML was induced experimentally only after a long latent period, it has been proposed that strain HPRS-103 of ALV-J does not contain an oncogene and was therefore more closely related to other slowly transforming strains of ALV [Payne and Fadley, Diseases of Poultry, 10th Ed., 414-466, (1997)]. However, acutely transforming ALVs were recovered from ML induced experimentally by HPRS-103 [Payne et al., Avian Dis., 37:438-450 (1993)].
The sequence of the complete proviral genome was reported to be a multiple recombinant of at least five ALV sequences and one endogenous avian retroviral (EAV) sequence [Bai et al., J. Gen. Virol., 76:181-187 (1995); Bai et al., J. Virol., 69:779-784, (1995)]. The HPRS-103 env is reported to be closely related to the env gene of the defective EAV-E51 but divergent from those of other ALV subgroups [Bai et al., J. Gen. Virol., 76:181-187 (1995); Bai et al., J. Virol., 69:779-784, (1995)]. The nucleotide sequence of the env gene of HPRS-103 was shown to have 40% identity with the corresponding regions of the other ALV subgroups [Bai et al., J. Gen. Virol., 76:181-187 (1995); Bai et al., J. Virol., 69:779-784, (1995)].
Venugopal et al. [Avian Dis., 41:283-288 (1997)] described the construction of a recombinant baculovirus containing the cloned DNA encoding the gp85 envelope glycoprotein of HRPS-103. They fused the env DNA to the carboxy-terminus of the affinity tag glutathione-S-transferase. Their fusion protein was secreted into the supernatant medium of the infected insect cell culture. Using the recombinant protein in ELISA assay, they found the assay to be specific and sensitive for detection of HRPS-103 virus-specific antibodies in the sera of infected birds.